text:
Is it an overkill to request to see airplane maintenance logs at a new flight school?
I'm getting a checkout at a new flight school, so I don't know anything about the maintenance records of their airplanes other than this school has been in operation for some time and so I assume everything is in order.  As PIC, though, I would think I would feel better seeing for myself that this plane I have never flown before is indeed up-to-date, at least in its required inspections.  I've never had an urge to do this before, I've always just trusted that the flight school is running things properly, but I guess since I have quite a bit more experience since my last checkout I felt like looking into this would be judicious.
Is this overkill?  Would it be taboo or send a message of distrust to the school if I asked to see the mx logs on my plane I'm getting checked out in?  Does anyone make it a point to do this?  Thanks in advance for your comments.

If they deny you then you should start worrying.

While I personally wouldn't bother, you should do that which makes you comfortable. There's also something to be said for the learning experience of finding out what maintenance is required and the recording requirements if you're not already familiar with such.

I'd refer to FAR 91.3(a):

The pilot in command of an aircraft is directly responsible for and is the final authority as to the operation of that aircraft.

Therefore, I believe you have a duty to determine that the aircraft is properly maintained.   While that doesn't mean disassembling it and checking the work yourself, I do think that its reasonable to verify that the maintenance logs have recent entries, and appear orderly.
At my old flight school, I never got any grief at all (and occasional complements) when I wanted to see the logs for some reason.
If they give you so much as an eye-roll when you ask to see the logs, that should be a cautionary sign.
I think it is also an easy way to meet the maintenance guys, and be introduced to them as a careful, thoughtful pilot.  (The Mx guys likely despise "cowboy" pilots who bring back damaged equipment, and don't report it.)  You'll get to know some people at the new school, and get a reputation right off the bat.

I like this answer; ultimately, it's your own life you take into your hands when you fly a plane, so assuming you still wish to do so there's not much I would consider "overkill" when it comes to ensuring the safety of the craft you will be flying.

Is it overkill? Probably.
Schools generally do a good job maintaining their aircraft (they're used hard, but kept airworthy because if they're out of service the school is losing money). Most of what you should be concerned about is stuff you should find on a thorough preflight. You would need some specialist knowledge to determine if a log entry is a "problem" or not (absent something like "repaired right main gear attach point and installed new right main landing gear assembly" showing up).
Most of the schools/rental outfits around here keep a status sheet with the aircraft's dispatch documents so you (and they) can easily see when required time-in-service or calendar-time inspections are coming due. If there isn't one I'd make a point of asking about inspections and such to be sure they've been done, but otherwise I'd be pretty trusting.
Bear in mind that there's nothing stopping an unscrupulous school or mechanic from "pencil-whipping" inspections. An aircraft can be perfectly airworthy on paper but full of "How could they possibly have missed that?!" maintenance discrepancies when you preflight it.

Should they let you review the logs with an instructor or mechanic if you ask? I think so.
If you want to do this you should let them know in advance so they can have the logs available.
Bottom line, as PIC you need to be sure that the aircraft is in an airworthy condition (which includes compliance with required inspections, ADs, etc.) and if you feel you need to see the logs to verify that it's your call.
Reviewing the logs probably isn't a common request for casual rentals, but particularly if you're taking flight lessons there spending some time and reviewing the maintenance records for an aircraft is a great learning experience.

+1 for the learning experience. I think thats the most important point. You should know what to look at and how to interpret it. You'll only learn that from someone qualified and experienced

I don't see it as overkill at all.  Not only is it your responsibility as a pilot to verify if an aircraft is airworthy, it may save your life.
For more info on why and how to perform a deeper first-review of a new aircraft you might be thinking about flying for the first time I would strongly recommend a wonderful M-Pamphlet published by the FAAST team called "Advanced Preflight".

Advanced Preflight refers to conducting a preflight that goes beyond the normal preflight checklist. This is accomplished by obtaining a valuable maintenance history of the aircraft and developing an additional items checklist. While developing the additional items checklist requires some time, once you have developed the additional items checklist it can be used in conjunction with the aircraft’s preflight checklist for all future preflight inspections.
Using the additional items checklist discussed in this M-Pamphlet will guide you through an enhanced preflight
  inspection to help reduce your risk of undetected maintenance problems.
  This M-Pamphlet provides information to owner/operators and AMTs on

how to conduct a complete review of all maintenance-related data on the aircraft you operate and/or maintain,
the steps in extracting the valuable information from this data, and
how to develop an additional items checklist to be used in conjunction with the aircraft’s preflight checklist for all future preflight inspections.

Whether you are an AMT or a pilot who owns, rents, or borrows an aircraft, Advanced Preflight is for you!
For the AMT, this pamphlet will assist in conducting a records review prior to beginning an inspection on an
  aircraft. This is vital if the aircraft to be inspected is new to the AMT.
For the pilot, remember to always use your preflight checklist. The additional items checklist does not replace
  your existing preflight checklist; it only enhances its use.

authors: Юля Николаева


text:
Where can the FAA versus ICAO official filed differences be found?
ICAO has a process where individual countries may file differences from the ICAO standard when the rules of the country do not coincide with the published standards.
Where can the list of differences that the FAA has filed be found?  I have found references saying that it is in the AIP, but I could not find a list in that document.
For instance, there is an ICAO requirement that certain aircraft are covered by a Flight Data Monitoring (FDM) program, but FAA rules say that it is an optional program and not required by 14 CFR.
I found one (expired) document, paragraph 4b which refers to the FAA filing a difference with ICAO and want to see a complete list of all current differences.

The link you provide is for an amendment of the US AIP, not the entire document.
The entire document is available here: (link)
You will have to look at section GEN 1.7 (starts at PDF page 57).

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

authors: Юрий Вавилин

sort: votes


text:
Which is the difference between IMA (B777) and Open IMA (A380)?
The integrated modular avionics concept (IMA) was developed by Boeing for its B777. Open IMA is an improved version developed by Airbus starting from A380. Which are the differences? For example, I got that the network is optical fiber for IMA and Ethernet/Avionics Full-Duplex Switched Ethernet (AFDX) for Open Ima: why?
I know that the question may be too broad and not very easy, so I would welcome even some links to deepen the argument.
Moreover I would like to understand: where is it used IMA nowadays? Only in B777, or even in B787 and new generation B747 and so on? Idem regarding Open IMA: only A380 or even in the A329 Neo?
If Boeing and Airbus have these new systems, what do you have in all other companies? Embraer, Eurocopter, Tupolev etc.

The primary difference is that the B777 is the AIMS (airplane information management system).  It is a Honeywell developed system where all the software on the systems is controlled by Honeywell (closed system).  The biggest downside to the closed system is maintenance and support.
The A380 system is a semi-open IMA system. It has a single supplier hardware cabinet with processor slices and an common operating system.  Different suppliers can develop their applications to run on the platform.
Most newer aircraft designs use the IMA architecture as it reduces the number of LRUs and saves weight.  Boeing and Airbus are going to more open systems.  B787 and B777X are open as is the A350, mainly for competition reasons.  Smaller aircraft (Bombardier, Embraer) are typically closed as they tend to have single source avionics (Rockwell Collins, Honeywell).

Pretty much. ;-)

Is this AIMS or IMA a controlling avionic system, like the fly-by-wire?

@AirCraftLover I'm not sure what you mean by controlling. The IMA hosts applications that control things - displays, hydraulics, environmental controls, etc. It's generally not used for the primary flight control system (FCS) due to criticality and speed needs. It does include the Flight Management Application which does interface with the FCS. The difference is instead of having all the suppliers show up with their own computers with software pre-loaded, there's an IMA server and the suppliers just bring software to load. It doesn't host everything, but it makes a difference.

@ymb1: Not quite, you can still boot Linux on a Mac.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How do I obtain permission to fly an airplane that isn't airworthy?
How do I get permission to fly an airplane with a non-safety-related airworthiness issue, like being out of annual or having an inoperative radio in order to take it somewhere that it can be fixed?

Contact your local FSDO! ;)

You must request a Special Flight Permit from the nearest FSDO (Flight Standards District Office).
You'll need to fill out Form 8130-6, Application for U.S. Airworthiness, appropriately calling out the reasons you need a SFP (ferry flight, etc). Once the form is submitted, you may be subject to an inspection by an FAA official or representative, verifying that your aircraft is in fact in a condition for safe operation.
Avemco, the insurance company, has a good article on ferry permits that might be worth an extended read and which I don't intend to copy here.

The FAA / Philidelphia FSDO already gave a perfect short and snappy official answer perfectly matching your question.
Please note the restrictions mentioned in this handy sheet to stay absolutely legal :)
The short summary: contact your local FSDO to request a Special Flight Permit ("ferry permit"), which are commonly used for:

Flying the aircraft to a base where repairs, alterations, or maintenance are to be performed
Flying an aircraft whose annual inspection has expired to a base where an annual inspection can be accomplished.
Production flight testing of new production aircraft.
To authorize the operation of an aircraft at a weight in excess of its maximum certificated takeoff weight.

and many other reasons detailed in the link above.
To obtain a special flight permit you will need to provide the following info to the FAA:

Purpose of the flight.
Proposed flight itinerary.
Essential crew required to operate the aircraft.
The ways, if any, in which the aircraft does not comply with the applicable airworthiness requirements.
Any other information they may request


text:
Which airplanes are exempt from Europe's 2015 CPDLC (Link 2000+) requirement?
In February 2015, all flights above FL285 in EU airspace are required to have CPDLC/Link 2000+.
However,  I have been told by an avionics provider that some aircraft types are exempt from the requirement.  Where can I find the complete list of exemptions?

The European Commission has published the Commission Implementing Decision of 9.12.2011
on exemptions under Article 14 of Commission Regulation (EC) N° 29/2009 (the CPDLC rule)
It contains the following table of aircraft that are permanently exempted from the CPDLC implementing rule.
╔════════════════════════════╦════════════╦════════════════╗
║           Model            ║  ICAO Id   ║ Marketing Name ║
╠════════════════════════════╬════════════╬════════════════╣
║ Airbus A318 - 112          ║ A318       ║ A318           ║
║ Airbus ACJ - 319           ║ A319       ║ ACJ 319        ║
║ Airbus ACJ - 320           ║ A320       ║ ACJ 320        ║
║ Airbus A330 – 200/300      ║ A332/A333  ║ A330           ║
║ Airbus A340 – 200/300      ║ A342/A343/ ║ A340           ║
║              /500/600      ║ A345/A346  ║                ║
║ British Aeropace AVRO      ║ RJ1H       ║ AVRO RJ        ║
║     RJ100                  ║            ║                ║
║ Dassault Falcon 10 and     ║ FA10       ║ Falcon 10      ║
║     Falcon 100             ║            ║                ║
║ Dassault Fan Jet Falcon    ║ FA20       ║ Falcon 20      ║
║     Basic and              ║            ║                ║
║     Serie C/D/E/F/G        ║            ║                ║
║ Dassault Mystère-Falcon    ║ FA20       ║ Falcon 20      ║
║     200, 20GF and 20-      ║            ║                ║
║     C5/D5/E5/F5            ║            ║                ║
║ Dassault Falcon 50EX and   ║ FA50       ║ Falcon 50      ║
║     Mystère Falcon 50      ║            ║                ║
║ Dassault Falcon 900, 900B, ║ F900       ║ Falcon 900     ║
║     900C and 900 EX        ║            ║                ║
║ Dassault Falcon 2000       ║ F2TH       ║ Falcon 2000    ║
║     and 2000EX             ║            ║                ║
║ Gulfstream GIV             ║ GLF4       ║ Gulfstream IV  ║
║     and GIV-SP             ║            ║                ║
║ Gulfstream G300            ║ GLF4       ║ Gulfstream 300 ║
║ Gulfstream G400            ║ GLF4       ║ Gulfstream 400 ║
║ Gulfstream GV              ║ GLF5       ║ Gulfstream V   ║
║ McDonnell Douglas MD11-F   ║ MD11       ║ MD-11          ║
║      and MD11-CF           ║            ║                ║
╚════════════════════════════╩════════════╩════════════════╝

Nice, ASCII art ;)

@roe I didn't find the markdown way to do it (there seems to be none) but I found a website that does text to ASCII table conversion. http://www.sensefulsolutions.com/2010/10/format-text-as-table.html . Still needed to adjust a lot manually though...


text:
Can light GA aircraft with FDs or couplers use the RVR reduction clause on an ILS?
If you are in a modern GA aircraft, you may have a flight director and/or autopilot that can be coupled to your ILS receiver.  (Certainly, this is true of GA glass...)
Some ILS approaches provide a clause (marked by the * on the minimums and in the notes box on the plate shown below) which allows the RVR minimums to be reduced from 2400 to 1800 if you are using a flight director, HUD, or coupled autopilot to fly the approach to the decision altitude.

Does this clause apply to light GA aircraft with the appropriate hardware (say a C172 with a G1000 in it), or is it limited to use by transport category/multi-crew operations?

FAA Order 8400.13C outlines these procedures. Section 7 c outlines the requirements for this procedure. Most of these affect the airport facilities or procedures themselves, and section 5 b outlines the IAP requirements for aircraft:

Aircraft equipped with an operable FD, or AP with an approach coupler, or HUD which is certified for operation to a minimum of 200 feet HAT are eligible for this operation.

There is also a note under 9 b:

Single pilot operators are prohibited from using the FD to reduced CAT I landing minimums without accompanying use of an AP with an approach coupler or HUD.

So it would appear that having a FD is not entirely sufficient; a pilot with a FD can use the reduced minimums if they also have one of the following:

AP with approach coupler
HUD
Copilot

So if I'm reading that right it appears the answer for our hypothetical Cessna 172 with the G1000 and coupled autopilot is "Yes, provided the approach coupling and autopilot are certified for operation to 200 feet height above touchdown, or lower."

However, section 9(b) of that order requires the "operator" to have OpSpec approval or special authorization (LOA). That's supported here: the C052 LOA applies to part 91. But this stuff isn't exactly a model of clarity :-)

It seems that the APs typically fitted alongside the G1000 do support operations down to 200' HAT, so yeah, using the AP to fly the approach would do the trick.

I'm 90% without diving into regs and manuals that, a coupled autopilot is not what a C172 has, even with a G1000. Coupled is almost always referred to with systems that have 2 AP systems that are coupled and will take over if one fails

@slookabill You are probably confusing requirements for AutoLand (which DOES require 2 A/P systems engaged) for a coupled approach.  Only one A/P is required, even in the Part 121 airline world, for an approach to be considered "coupled."

@Pondlife Indeed, it's not clear how one would go about getting LOA C052 issued as a part 91 operator (particularly with the required training bits) - A trip to the FSDO with a cask of your finest drinking stuffs may be required to make it happen.

Rereading your link @Pondlife -- it looks like C052 is not available for normal Part 91 operations...but then again, is it needed to begin with?


text:
Where can I find an ATM simulation software to investigate traffic flow capacities?
Does anyone know what software is suitable to investigate air traffic flow capacities in various FIR's / routes. I need to see the effect of temporary reserved ares due to military activities, weather, changes of routing due to LOAs. Taking into account meteorological data would be advantage but it is not necessary.
It would be great if it will be possible to emphesize (colours, histogram, ...). usage of FIR areas.
What kind of software tools are used by EUROCONTROL or ATM consultancy firms providing this service. What standard tools commercially available (or for free)?

What do you want to investigate by simulation? If you want to investigate noise impact you use a different simulator than when you investigate throughput or conflict probability. Do you need to distinguish between aircraft types? Aircraft load factors? Airline operating procedures. Is wind a factor to take into acount? Thunderstorms? Air traffic control flow restrictions? Please clarify.

I need to investigate capacity usage in a different FIR areas/routes. How it will afect temporary reserved ares due to military activities, weather, changing current route due to LOAs. Meteorological data would be advantage but it is not necessary.It would be great if there will be possible to emphesize (colours, histogram, ...). usage of FIR ares.

This question appears to be off-topic because it is about selecting software packages. Currently there are 1836 questions about Mathematica usage at maths.se so you might consider composing a question for that Q&A site.

Well this is special aviation software. It is difficult to use some general mathematical SW. Ok, I redefine to my question - which SW use EUROCONTROL or local bureaus experts for this simulation?

It might help to write in the Q in what ways Simulink, ComDATSS etc are not appropriate. (n.b. to redefine your question it is best to use the "edit" link under the question text)

On hold because my question is unclear? I think my question is clear enough and I sad exactly what I am asking for... Anyway, I have already found answer for my problem. ACES and FACET from NASA Aviation System Division solve my problem. It should handle all statistical data, it has statistical output as well and it could also handle meteorological data. Currently this SW use FAA and some airline companies to modelate ATM concepts (http://www.aviationsystemsdivision.arc.nasa.gov/).

Suggestion: If you don't think your question or answer will be of any help to other people, you could just delete the question. I think it would be better if you would add your answer (from your comment) below, elaborating a little, then accept it in a day or so.

RedGrittyBrick: I wanted to answer my question but it was on hold and I couldn't add it. One suggestion for you: you should post only related comments/answers. If you don't have enough information or you don't know answer you should postpone commenting. It is not related to math SW (trust me - I really made research about this problem) and if you don't think so, write answer with example. Otherwise, you are doing confusion.

"which SW use EUROCONTROL [use] for this simulation?" They have teams of developers to make these softwares for them.

I have already found answer for my problem. ACES and FACET from NASA Aviation System Division solve my problem. It should handle all statistical data, it has statistical output as well and it could also handle meteorological data. Currently this SW use FAA and some airline companies to modelate ATM concepts (aviationsystemsdivision.arc.nasa.gov).
Thanks for all your help!


text:
Is an engine surge classed as an engine fire?
Sometimes flames come out from the exhaust due to bearing distress or turbine blade fracture.
Can such flames/fire be considered an engine fire?

If the fire is momentarily and stops by itself: No, this is not an engine fire. Flames can come out of the engine at both ends in a compressor stall (also called surge - watch the movie which is linked in the question!), but that is no engine fire. See this question for another example where spectacular flames develop, yet the engine is not on fire.
If the fire can only be stopped by shutting off the fuel supply or the engine itself: Yes, that is an engine fire. I guess you refer in your question to this bulletin on PW4000s, where the No. 4 bearing overheated due to insufficient lubrication. In that case the oil itself overheated and burned, but this still makes it an engine fire.

How can we categorize different fires in engine such as Oil fire, Fuel fire, Hydraulic fire and fire which is caused by internal engine damage?

An engine fire is always detected by the fire sensors, however to the contrary it happens to get false fire alarms due to pneumatic leaks.

Engine surge or stall occurs when there is a breakdown in smooth flow of air through the jet engine compressor.
It can be caused by incorrect airflow control within the engine itself by faulty scheduling of  Inlet Guide Vanes (IGVs) within the compressor or overfueling during acceleration due to faults within airfuel control. Ice ingestion or heavy bird ingestion may damage the compressor by disrupting airflow and creating a surge in extreme cases. Surges may be recognised as burbling or popping in mild cases with airflow disruption within one or a couple of compressor stages only, or large explosive bang in extreme cases of compressor or turbine damage.
Surges in flight may occur at altitudes depending on throttle handling and type / generation / condition / cleanliness of the compressor or airplane involved. Fire breakout is not the normal consequence of an engine surge unless there is severe damage by failure of a rotating part at high power. Perfection of design, materials and computerized engine control has reduced surge events dramatically over last 15 years or so.

Hello konkorde, welcome to Aviation.SE!


text:
Why isn't the last known position of a black box continuously available?
I have read that some GPS satellites receive this data. Where is that information recorded? Why would it not be used? Inmarsat covers all but the polar regions, why don't the airlines use that system to transmit and track aircraft location data? I don't think that cost would exclude this, as a crash is hugely expensive, especially counting downstream costs (search and recovery, collateral damage, etc.).http://www.inmarsat.com/about-us/our-satellites/our-coverage/

GPS satellites do not receive data.  They only transmit.

This is a much-too-broad question. The FDR/CVR's purpose and their technology are completely different than the Inmarsat which itself is completely different than GPS. None of them, in their current designs and purposes are for real-time communications (reporting) of the location of something TO someone else.

This question is set to be closed by giving one example as duplicate that is closed...


text:
Why do planes always land on rear wheels instead of the nose wheels?
Various times, I have seen and felt myself that the plane always lands on the rear wheels, but not the front wheels. Why do the pilots land it on the rear wheels instead of the front? Does it have some advantage to it or is it a rule?
Is this required for all the planes (irrespective of size, type) to land only on the back wheels?

There are even planes in which you can't choose on which wheel to land at all: http://www.planes.cz/photo/1090/1090849/l-13-blanik-ok-1856-slovacky-aeroklub-kunovice-uhe-lkku.jpg

It is quite possible to land nose-wheel first.  One of my past partners did this in our Cherokee some years ago.  Bent the prop all to heck, and required a complete teardown & rebuild of the engine.  Fortunately most of the cost was covered by insurance.

@PavelPetrman: What is that, a U2 landing trainer?

@dotancohen: L-13 'Blaník' glider of Czechoslovak origin. It's quite possible you are right, since USAF seems to have been interested in the successor and have purchased some.

@PavelPetrman: Judging by the years I don't think that the US would have been training new U2 pilots on that machine. Only South Korea I think might have still trained new U2 pilots in the early 2000s. But those are really interesting links, and it seems that glider is a popular model. I've never seen them in Israel.

@dotancohen: I'm not that much into military aircraft, you see, so the joke went completely wasted on me, sorry:-) The type is really popular in Europe, although currently grounded for technical reasons. My father is on some of the photos from the USAF and has won several trophys in aerobatics on this plane (and, for one, taught aerobatics to Martin Sonka from Red Bull Air Race), that's why I'm so fond of this particular one-wheeler.

It wasn't even a joke. The U2 had "bicycle landing gear", the wheels were close together on the fuselage similar to the Blanik. That is cool to know that is your dad in the pics!

It is for much the same reason as when you jump off a wall you try to land on your feet rather than your hands... Your nose regrets it afterwards. :)

@PavelPetrman : No, it's not a one-wheeler, it's a taildragger. It lands on both the main and tail wheels the same time. If one of your wheels touches ground first, it means you did a less than perfect landing. There are many other taildraggers, including aircraft with 2 front and one tail wheel.

Begs the question - what airframe designer/manufacturer is credited with the first retractable landing gear system?

@Everyone: ask a new question, not here in the comments ;)

Always is not correct. There have been generations of tailwheel-type landing on their main gears which were on the front.

Google bicycle gear, B-47, B-52. W/ this configuration both wheels leave ground about same time on takeoff, and landing may be nearly simultaneous on both gear as well.

Aircraft land on the main wheels. For aircraft with nose wheel it is the back ones, but for aircraft with tail wheel (also called “tail-draggers”) it is the front ones. In either case the main wheels are very close to centre of gravity and carry most of the aircraft's weight, the nose or tail wheel only carries a small fraction of it.
The aircraft must land on wheels that are close to the centre of gravity (longitudinally). If they were not, the force on the wheels would create a moment that would violently pitch the aircraft. Actually, tail-draggers tend to bounce on landing a bit because there still is some moment left and in case of tail-draggers it pitches the aircraft up.
Early planes were almost all tail-draggers, because that layout is more robust, handles unpaved runways better and has less drag when the gear is fixed. It however provides poor directional control especially once the tail lifts off the ground during take-off roll. Later most designs started to use nose-wheel, because it provides better directional control, is directionally stable, makes the floor level when the aircraft is standing so loading is easier and visibility during taxi is much better and with invention of retractable landing gear the drag didn't matter any more.

If a wheel to the rear of the center of mass touches first, any pitching motion will try to turn the plane toward the direction of motion.  If a wheel ahead of the center of mass touches first, any pitching motion will turn the plane away from the center of motion.  While neither sort of violent pitch change would be good, the former is self-correcting while the latter isn't.

@supercat: That's one of several reasons aircraft with nose wheel (and therefore main wheels aft of CoG) are easier to handle than tail-draggers (with main wheels ahead of CoG).

Could you add an explanation of what "tail-draggers" are?  It's unclear to me which wheel formation this refers to.

@Kyralessa: There is a picture already in the other answer below.

I was flying tail-dragger gliders and we had to land on both the main and tail wheels. In a perfect landing both the main and tail wheels had to touch the ground the same time.

Many tail-draggers, especially warplanes with bigger engines and props, also have a massive blind spot directly in front while taxiing, which is a liability whenever there's no spotter to guide ground traffic (a common situation in gen-av).

It's also worth mentioning that the wings-level attitude on the ground of a nose-wheel airplane also gives it less drag on the ground, resulting in a shorter take-off roll.

And a taildragger configuration is next to useless for jets, as the jet exhaust hits the ground and deflects upward over the tail, blanketing the elevators and making it very difficult to lift off (the pilot generally has to tap on the brakes momentarily to pitch down to level and allow the elevators to work properly; you can probably see the dangers inherent in doing so).

Jan Hudec already gave an excellent description of why the gear configurations are designed as they are. Another important thing to note, though, is that because aircraft are designed to land on their main gear, the other gear (nose gear in tricycle configurations or tail wheel in tail draggers) is not designed to be able to take the force of a landing. Landing on the nose gear in an airliner will most likely cause the nose gear to collapse, leaving you in a situation like Southwest Flight 345:

Image Source: New York Daily News
One of the passengers on that flight recorded the landing and posted it on YouTube. While there were only a few minor injuries (mainly from using the slide at such a high angle, if I remember correctly,) the aircraft received such substantial damage that it was written off. Obviously, that is not a desirable outcome, so airlines usually prefer their pilots to land on the main gear instead.
By the way, when we talk about a tail dragger, we're talking about planes with a landing gear configuration like this:

Douglas DC-3. Image Source: Wikipedia
Whereas tricycle landing gear refers to the configuration you're probably used to seeing that looks like this:

Boeing 737. Image Source: Wikipedia

The link to Southwest 345 was recently updated to a page about the specific accident (which is great,) but unfortunately that page on Wikipedia has been nominated for deletion. In case it does get deleted, you can still read about it in the Accidents and Incidents section of the Southwest article.

One quick comment regarding the previous discussion on tailwheel aircraft. Taildraggers actually have two landing techniques at their disposal.
The one most people envision, where the aircraft touches down on the mains before gently settling the tail down, is called a wheel landing.
There is, however, also the three-point landing, where the goal is to touch down with all three wheels at the same time and is usually the first landing technique taught, especially to pilots transitioning from tricycle gear aircraft.
The technique used on each landing is chosen based on a number of factors, among which:

Landing type (e.g. short-field vs. cross-wind)
Aircraft type (some aircraft are just plain more difficult to land or may be entirely unsuited for one technique versus the other)
Pilot currency (with the exception of heavy wind conditions, I find three-points easier to "grease" when out of practice)
Runway conditions (pavement is much less forgiving then grass of sloppy rudder control; by the same token, three-points can offer better debris clearance for the propeller on rough fields)

If you want to learn more about aircraft and flying, I would encourage to look up FAA resources (especially the FAA Airplane Flying Handbook), as well as the trove of information on AOPA's website.

In an approach an airplane is generally descending between 500 and 1000 feet per minute, that's a minimum of 8 feet per second. That may not sound like much but just hitting the ground at that rate of descent would lead to a big bounce and possibly damage the airplane.  It would certainly be uncomfortable for the passengers.
In order for an airplane to land softly, it must decrease its rate of descent, to do this the nose is raised in a maneuver called a flare. A nose-up attitude will, in a tricycle configured airplane, bring the main (rear) wheels in contact with the ground first.

Taildraggers flare but land on the front wheels. Landing on the mains has nothing to do with the approach or flare. We do it to have a controllable landing and avoid collapsing the nosegear.

Taildraggers don't have nose gear obviously, I'm not sure the point you're trying to make @casey.

True, the nosegear collapse is specific to tricycle gear, but the rest of that sentence is general. My point was we land on the mains because they are load bearing, not because of the way the approach and flare are flown.

I understand you. When I read this question I interpreted it as asking why airplanes land in a nose up attitude rather than placement of the gear. As the question of gear placement was already well covered I saw no point in rehashing it.

Not all, taildraggers will land on the front 2 wheels.
Because then the plane doesn't wheelbarrow off the runway. Have you ever tried running with a wheel barrow? The smallest deviation of forward will get expounded and before you know it the thing will be off to the side.
Landing on the rear wheels will put the center of mass forward of the drag source so deviations left and right will self-correct. This plus differential braking will allow greater control over the aircraft.

In most large aircraft, you'd be more likely to collapse the nose gear than to wheelbarrow, I would think.

Taildraggers usually land on all wheels at the same time. Even if they land on the front wheels, the tail wheel follows very quickly.

@vsz - If that's true, I've been landing taildraggers too fast.

@SteveV. https://www.youtube.com/watch?v=OXyVW2UMCK8 There might be taildraggers which have to be landed on their first wheels by design, but I've never seen any. I personally only know about 3 types, and all 3 of them have to bee landed on all wheels the same time.

@vsz - https://youtu.be/sLBHblJNFQE?t=4m29s 14 seconds from mains to tail touchdown.  Not my video, but this is how I usually land.

Just for completeness, there's also the B-52, which has "bicycle" landing gear (both the front and rear are considered "main" landing gear). I believe the ideal when landing it is to have the front and rear gear touch down simultaneously1.
For any who care, here's a video of a B-52 landing, showing the nearly simultaneous touch-down of front and rear gear.
As an interesting aside, to support crabbed cross-wind landings, both the front and rear main gear of the B-52 are steerable, so it can land (or take off, taxi, etc.) with the nose turned up to 15 degrees from the direction of movement. Here's another (from the front) showing a crabbed landing.

1. I originally wrote that as "all the gear", but that would be false. It also has tip protection gear that normally touch down quite a bit later. Its wings are quite flexible, so the tip protection gear don't normally touch down until it slows down enough that the wings are producing substantially less lift. If it's carrying a light fuel load, they might not touch even then.

Just when sitting still on the ground, the B-52's wings could/did flex by around 10 feet at the tip, depending on fuel load. In flight, they could flex upward still more for a total of around 17 feet of flex (over a wing span of roughly 165 feet).

No reason to use the past tense, the B-52 is still flying and still landing on all 4 at the same time.

@OSUZorba: Good point--my personal involvement is past-tense, but they're still going strong.

I am going to answer this in another way.
Generally this is by design. The wheels are not the real issue, the angle of attack is.
When most aircraft land, they are "flaring" or pointing the leading edge of the wings as high as possible without getting into stall territory.  This is especially true for hang gliders and parachute canopies, even though neither of these have wheels.
It is called flaring as this is what it is called when birds land. (Ducks, Pelicans etc.)
In this aspect, a nose wheel is going to be higher, and hence touch down last.
Even a tail dragger is looking at this until the last moment. It's really a powered glide.
A pilot will avoid a stall, look for "ground effect", and be mindful of recovery options.
The design of the landing gear reflects this strategy, if a commercial ariliner touched town nose first (levelish) it would be travelling faster and experience more of a shock, the gear would need to be much heavier. This type of pancake landing does not usually end well.

Your "rear wheels first" observation pertains to aircraft with "tricycle" landing gear. For various reasons, the landing gear of such aircraft is configured so that they sit more-or-less level on the ground (when parked or taxiing). Such an aircraft usually cannot take off or land in such a level attitude. This is because the wings won't generate enough lift unless the aircraft is at or near cruising airspeed. To minimize wear and tear, danger, and runway length, takeoff and landing is performed at the lowest possible speed, allowing for a safe margin above stall. To fly at such speeds, the wing needs a high angle of attack, which means the aircraft has to be pitched into a nose-high attitude. To make the landing a positive transition, aircraft "flare"; essentially pitching up higher and higher and slowing down more and more while just above the runway until the wing essentially "stalls" - loses lift. At this point, the aircraft settles onto the runway at the slowest possible speed and should stay in contact with the runway (not "bounce" or "balloon" up). All this amounts to touching down on the main gear first.
It is certainly possible to touch down on the nosewheel first - a term called "wheelbarrowing". This is very dangerous. Firstly, it could only occur if the approach was flown too fast - more speed means more forces and things going wrong more quickly. Second, the aircraft is touching down on a point ahead of the center of gravity. The slightest sideways motion will create a lateral moment that could (and probably would) spin the plane around into a crash.

Tricycle vs taildragger

Is this required for all the planes (irrespective of size, type) to
  land only on the back wheels?

All aircraft touch the runway on their main gear, and the main gear is at the level of the wing. Adding a wheel aft or forward of the main gear leads to two configurations with a noticeable difference: The angle between the wing and the horizontal plane when the aircraft is on the ground.

Those with a nose wheel and a low angle, the vast majority of today's aircraft, and all commercial airliners. This gear configuration is named tricycle.
Those with a tail wheel and a high angle, a category which was used at the beginning of aviation. This gear configuration is named taildragger.

Source
The advantage of the tricycle is the stability on the ground, thanks to the engine being located between wheels. The inconvenient is that takeoff cannot take advantage of the weight of the engine to help rotate the aircraft. Elevators are more solicited. If the rotation is not executed correctly, a tailstrike can occur.
Tricycle aircraft landing

Does it have some advantage to it or is it a rule?

It is a technical requirement. When landing, the aircraft must touch the runway with a very small vertical speed, the glide path must slope gently down. The weight of the aircraft pulls it down at an accelerating rate (free fall), the aircraft must oppose this acceleration by generating lift.
Lift is proportional to airspeed and to the angle between the direction of the aircraft and the direction of the wing (the wing median line, named the chord line). This angle is named the angle of attack. The angle of attack obviously depends on the aircraft attitude (pitch angle).
When landing a tricycle aircraft the pitch angle must be relatively high, so that the nose gear doesn't touch the runway before the main gear. At the same time a fair amount of lift is generated due to the correspondingly relatively high angle of attack, as depicted in the left hand side of this picture:

In contrary, if we wanted to touch with the nose gear, we would need to strongly decrease the pitch angle. Such attitude automatically decreases the angle of attack, and the associated lift (right hand side above) which is already low due to the low speed required for landing.
If the lift is insufficient to counteract the gravity acceleration, the aircraft descends too quickly, and the vertical speed at touchdown creates a force on the gear exceeding its mechanical strength. Damages occur.
This is the reason airliners, which are tricycle aircraft, don't land on the nose wheel. However this leads to another question: Why do we use tricycles instead of taildraggers? Looking at the first picture, we see it would be uneasy to board and deplane, due to the floor slope, but there is more to know, maybe another good question to ask.

its is called a flare, it is a 5-10 degree pull to slow the aircraft down and put the rear wheels on the ground.
The Rear landing gear is put down first because there at the center of mass (CoM), It is also smoother and safer. It is safer because the front landing gear is not made to hold the whole wait of the aircraft. (EX. the airbus A380 has many Rear Gear but only 1 front gear(http://avimotive.com/wp-content/uploads/2016/01/a.jpg))
It is smoother because It slows the sink rate.

While there is certainly a lot of truth in the above answers they all sort of treat the question in a fashion similar to: "Why does water freeze at the top and work down? Because otherwise fish would freeze." While there are a number of reasons why landing on the back wheels works better the single most important one is that when airplanes land their nose is higher than their tail so their back wheels are closer to the ground. The reasons for this is because as planes slow down their wings generate less lift. They have to do something to make their wings generate enough lift despite the airspeed reduction so as to keep flying else a sub-optimal condition involving bent metal and maybe fireballs will occur. They do this by pointing nose up which increases the wings' angle of attack and by changing the shape of the wing (flaps and slats) to make the wings generate greater lift at the expense of introducing more drag. By the time that they get close to the ground they have slowed as much as they dare which means that the speed alternatives are being used as much as possible. That means that the aircraft is leaning back as much as it safely can and flaps are fully extended. Right at the point that a safe landing is guaranteed then the greater danger to the aircraft's safety shifts from falling out of the sky to hitting the ground at too fast a speed so the pilot does things to dump speed. That means leaning the plane back just enough to increase air resistance but not enough to make it bob up in the air. A good pilot does this just a very few feet above the ground and adjusts things so that the plane levels out for a few brief seconds as the speed bleeds off. A not so good pilot briefly gains altitude and then the plane falls out of the air from 10 or 20 feet up and the passengers get to experience three or four very short flights before the plane finally settles down on the ground. All of this puts their back wheels closer to the ground which means that's where the rubber meets the road.

Aircraft land in nose-high attitude, but for long that simply meant the front gear had to be long enough and the aircraft landed on the front gear. So it's not the reason.

We only need increased lift very briefly to arrest the descent. We are not slowing down during the final approach (or shouldn't be, at least.) In light planes where we can flare more quickly, we fly the plane with a nose-down attitude all the way to the threshold, then quickly arrest the descent as we cross the threshold and numbers. All of the remaining flaring (and the landing on the mains) is solely due to our desire to land on the wheels that are designed to take the weight, rather than on the nose gear and/or the prop. It has nothing to do with a need for lift.

The reason that we flare slowly after arresting the descent is precisely because we don't want too much lift (or we'd rise back up off the runway, as you mentioned.) We're bleeding off speed there precisely so that we can land with the nose high (and, therefore, on the main gear.) Landing on the mains is the goal with reducing speed as a necessary precondition, not the other way around.


text:
What are the requirements of ferrying a spare engine?
It was not uncommon in the 60s and 70s to have B747 ferrying a spare engine.

(source: Australian Aviation)
Was that allowed only on aircraft specifically designed with a pod, or was that possible to add the equipment on any B747. What is the regulation applicable? (in the US for instance).
Additional question: is this still commonly used today in civil aviation?

related: http://aviation.stackexchange.com/questions/8339/off-wing-jet-engine-transportation

@ratchetfreak: The image selected seems quite popular :-) Great addition, I didn't know one engine could be removed and replaced by an unused spare one.

Hmm a brief search reveal nothing solid but most recently seen one is with Qantas and it is optional from production time. Most comments state speed limit (250knots) and range leads to decline in practice. Note the 400ER is not certified for 5th pod. Anyone got maintainence manual to confirm all this?

@mins - although it's tricky to do in-flight

@NobodySpecial particularly if the engine to be replaced is on the other wing.

It's a manufacturer option on some larger planes - basically adding a bit of structure and some attachment points. And it's expensive enough that airlines think about it.
Today's engines are much, much more reliable than the ones used in the 1960s so the need to move engines around by bolting them on to the next thing going that way is not what it once was. There is also a larger air cargo market, and it's likely cheaper in general to put the replacement on a pallet rather than under a wing.

Was also done with the L-1011.
I've never seen this done with a DC-10. Has anyone seen that?
https://i.sstatic.net/6vWS7.jpg


text:
Why was a flight delayed because of a bird in the cockpit?
This Washington Post article is about a Delta Airlines flight that took off after an initial delay, before turning back again shortly after, because of a bird that managed to stowaway in the cockpit.
My questions,

Would it be dangerous having the bird in the cockpit?
Was the decision to turn back expected or over the top?
Do Delta regulations (or relevant regulations) actually cover something this specific, or would it have been under some catch-all? If so, what would that be?
Have there been any similar incidents?
Does this ever happen on small private aircraft?  (It's not unheard of to find a small bird sitting in your car for some reason - maybe it's the same?) Has it ever happened to anyone here, what's the outcome?

and mostly,

Why didn't they just kill it?

(Aircraft kill small birds by the thousands, I mean - chicken was probably served on board.)

There was a case of a stowaway cat on an ultralight airplane:  https://www.youtube.com/watch?v=J_8mdH20qTQ

I once found a mountain bluebird in my Cherokee, when I left it parked with the vent window open.  Got it out before taking off, though.  More common is birds nesting in the engine...

Another way to ask the first question is "is it as dangerous thing having a tiny dinosaur in the cockpit?" The answers kinda flow from there.

You should include a small summary of the story you linked.

If this was an international flight then there could have been issues with undocumented livestock movements.  Even between states, it could transfer pathogens to an area that was previously clear.  This is a high priority for an island nation.

SE has linked this question to https://aviation.stackexchange.com/questions/14759/does-sex-occur-in-aircraft-cockpits-and-is-this-safe and from the title, I wondered if it was the same subject.

The flight was from Detroit to Atlanta (domestic flight, 2 hours) for people curious about international ramifications.

The probability of birdstrike is infinitely more when THE BIRD IS INSIDE THE PLANE!

There's also the possibility that the bird knows more about flying than the pilots do.

There were good edits that removed the clickbaity title and clarified events. Why revert them to to a poor title and a less informative body?

@abelenky That video really makes you wonder what kind of preflight checks that pilot did. If any. Did he check to make sure that the wings were still attached, for example?

@Fattie I rolled back your question because it was in a better state than the most recent edit.

@MichaelKjörling Cats can move--perhaps it avoided him while he was doing the preflight.  Or he could have preflighted, then gotten his passenger--and the cat got in during that time.

@LorenPechtel True, especially that the cat may have avoided him, but if I saw something moving on an aircraft, even just out of the corner of one eye, during the preflight, I'd darn well look more closely before dismissing it. So the cat would have had to really avoid the pilot in that case; and it didn't seem particularly inclined to avoid being seen after takeoff... Either way we can guess all day and not come any closer to an explanation for what really happened, but I do sincerely (for everyone involved) hope the pilot learned a lesson from the incident!

Re "and mostly, -- Why didn't they just kill it?"  -- Please elaborate to add details.  Do you mean, like, using the sawed-off shotgun that most pilots habitually carry on long flights?  Or using some other means?  Or-- ???  PS -- "Aircraft kill small birds by the thousands"  -- gets my vote for most irrelevant comment ever attached to any ASE question or answer.  Do we award some sort of prize for that?

Quiet, if you've ever had to catch say a pet small bird in a room, it's pretty easy, they usually just tuck up to one corner or nook. Then you "take it in your hand".  (Sure, if a bird's flying around in a basketball arena or such, one can't catch it.) As others have pointed out, you don't want the copilot (or whoever) wiggling around trying to grab a bird in a cockpit while you're flying along. However it's unclear in the stories if birdie was there while they were sitting on the ground; it would be trivial to grab it while still at the gate.

Regarding your second comment section, there was an implication in some stories that one wouldn't want to kill a small bird, that there was an animal welfare issue. IMO that would be absurdist. That being said, you can see it being a "PR nightmare" new story, "pilot squishes sparrow like spider..."  (I'm not sure what you mean by "Do we ..."; as far as I know you and I (we? some other grouping?) neither operate this site nor give awards.) (If you are one of the site operators, fair enough.) (If your sentence was some sort of joke - cheers.)

(Funnily enough our pet budgie recently passed on to a better place, RIP.  This QA being regurgitated gives me a tear!)

Having a small bird in a cockpit, or anywhere on board, would not be a problem during a normal flight because a normal flight should have a wide safety margin.
However, a situation can change extremely rapidly from safe-and-normal to heavy workload to full-emergency due to any number of factors, including weather, mechanical issues, airspace/congestion, etc.   In a high stress situation, a small bird could be the proverbial tipping point.  So I see and understand the decision to turn back.
It is remotely possible that a small bird could get somewhere it shouldn't, like behind a panel or near electrical lines and cause a short or other serious problem.  Its not terribly likely, but with 100+ lives at stake, why would you risk it?
As for why they didn't just kill it:  Killing it involves catching it, and catching a small bird while still flying a plane is not easy!!

Ah, you mean like the "chain..." that leads to a disaster.  Fascinating insight...

"Killing it involves catching it, and catching a small bird while still flying a plane is not easy!!" ...and one thing you certainly don't want to do in a cockpit in flight is start flailing around trying to catch a bird which is now doing its very best to avoid you, all the while everything is moving at 700-800 km/h...

Yeah, kill it how? With the shotgun you have under your seat?

@DonBranson Killing a small bird once you've caught it probably isn't that difficult. Catching said bird, on the other hand...

@MichaelKjörling - indeed. Also, remember to wash the salmonella off your hands once it's dead.

Note that the USA has not had a commercial aviation death in the last 8 years. You don't get that kind of record by taking unnecessary chances.

Besides, that damn chirping could drive one to distraction. I am certain that Bob Hoover could have solved the problem by turning the aircraft upside down (deadstick) quickly enough to knock the creature out and then complete the roll with the bird landing into the glass that he always seems to keep on the panel. Then release the bird on landing.

If it's a small bird bedded down quietly under the jumpseat, I don't think I'd worry about it too much.  Presuming that you found out about it while up at altitude, the question is, are you safer cruising for XX minutes to get to your destination, descend, and land, or are you safer cruising for a shorter time while you return to your departure airport, descend, and land?  Either way, the bird is in the cockpit for a descent and landing somewhere, and if it seems to be quiet & unobtrusive, I don't see significant risk in the extra time at cruise.
On the other hand, if the bird is wildly flapping around & being an annoyance & a distraction, then minimizing the time that you're putting up with that would absolutely be worthwhile.  Even small birds have enough beak & claws to scratch skin, and I wouldn't trust a scratch from any bird not to become a nasty infection.
I think something like this falls entirely within the realm of captain's best judgement -- I've never seen any written guidance at anything approaching the level of "consideration for a bird in the cockpit (discovered after takeoff)".
I'm also drawing a blank for anything similar in recent history, although I suspect that somebody somewhere has probably seen something pretty close.  When the major U.S. airlines log multiple millions of flights each year, even the really rare cases tend to come up now & then.
As for "just kill the bird," I suspect that the hard part of that plan would be in the execution of it (the plan, and the bird too, I guess).  If it's a fly buzzing around the cockpit, a good smack with the paper copy of the dispatch release will do the job, but for even a small bird, it will take more than that -- which tends to have its share of risks when wielding small improvised weapons in a confined space full of glass screens & instruments, circuit breaker panels, and another pilot whom you'd really like to avoid injuring!
It would be tempting to try to shoo the bird out of the cockpit -- either into the passenger cabin (which has its own concerns -- how long do you leave the door open waiting for the bird to fly out), or opening a cockpit window (at low altitude -- you can open them with sufficiently low pressure differential) & getting it out that way.  Of course, in an MD-90, you might have just given yourself a bird strike in an engine that way, so maybe just landing to deplane the fowl passenger would be the better option!

A great answer, thanks!

They were still climbing out when they found the bird. It was only abt 20 min from takeoff to landing. If they'd found it half way through the flight (as some passengers were falsely claiming) then I could see continuing on.

Nothing in the QRH then?

@MartinJames  No, not in the one my airline uses.  Nor in the generic Boeing QRH either.

Defowl the plane.

I disagree with the first paragraph of your answer. Even if it's sitting somewhere quiet and unobtrusive, it could get up and start being annoying - and there's been a study which won an ig-nobelprize for noting that the longer an animal has been sitting down, the more likely it is to get up sometime soon. While not per se dangerous in a normal situation, if some other abnormal situation comes up (turbulence, technical failure, etc), ANY distraction can be a serious safety hazard.

@TomMcW Technically, if the flight (from takeoff to landing) only lasted about 20 minutes, there's a pretty big chunk of that which certainly could qualify as "half way through the flight" for the purposes of bird detection. Even with an error of just a few minutes on the part of a passenger's estimate, we're now talking (for, say, ±3 minutes error) between 7 and 13 minutes into the flight; six minutes out of a 20 minute flight being a good 30% of the flight time.

I'm inclined to agree with @Lolgast. Also, more importantly in this case, situations that result in high pilot workload (even something relatively mundane as a bit of turbulence) appears likely to be the exact kind of situations that would upset even an otherwise calm bird, thus risking to immediately greatly increase pilot workload at an already somewhat bad time. I probably wouldn't trust it unless it can recite the safety briefing and is wearing its seatbelt correctly.

"It would be tempting to try to shoo the bird out of the cockpit -- either into the passenger cabin (which has its own concerns -- how long do you leave the door open waiting for the bird to fly out)" Someone, somewhere, just came up with a new terrorist plot for their next movie...

@MichaelKjörling I guess I said that wrong. The article said the passengers claimed they were "half way to Georgia" when the bird reappeared, when in fact they were only airborne like 5 minutes.

Don't forget the fact that if they were flying to another country (or maybe the bird originated from another country) there could be issues of Bird Flu spreading around. Killing it would be very unhygienic and could spread disease etc through the air con system. Also the crew could become ill if the bird dropped its guts all over the place.
Turning back to the airport would be a judgement call but most pilots would definately do it. When the workload is high the bird would also be a huge distraction and finally, if there was an incident the question would be asked "So you had a bird flying around the flight deck...why did you not RTB?"


text:
What happens to #2 if a formation flight violates a FAR?
In a formation, it's generally accepted that the lead pilot is responsible for safety of flight and navigation.  #2 is, colloquially, responsible for not hitting lead.  That is to say, in close formation, you never take your eyes off lead.  In many situations, #2 may not even be in radio communication with lead or monitoring ATC frequencies and his overall situational awareness will be degraded.
If lead, who is responsible for navigation, takes the flight into protected airspace (i.e, flies into Class C airspace without first establishing two-way radio communication) would both pilots be violated, or just lead?
For clarification:
The regulations governing formation flight are pretty sparse.  FAR 91.111, 91.146 and 91.153 are the only mentions of formation flying in the regulations.  There is no requirement for communication during the flight - 91.111 just requires that all pilots agree to operate in formation.  It is not unusual in a formation flight for lead to be on one frequency (talking to approach), and the wing to be monitoring another (or not monitoring at all).  Most communication is done via hand signals.  I do know that ATC treats formation flights differently - they effectively treat it as one aircraft (ATC Manual 2−1−13).  If the flight is cleared to land, both aircraft a cleared to land - #2 does not need to acknowledge.  Hence the question who is responsible if the flight (a single aircraft in the eyes of ATC), violates an FAR?

I don't know of any rule that says that an aircraft flying in formation that is not the lead aircraft is allowed to disregard ATC instructions. Usually ATC will issue instructions as "Flight of X, do Y", in which all aircraft are required to comply. All aircraft in formation must coordinate with each other, so they have to, by definition, be in communication with the lead and the other aircraft.

Joe, can you site any specific regulations for this? Im with Ron, I do not think that planes flying in close formation are governed differently.

Are you talking about simple formation flying, or aerobatic displays? If the latter, its highly unlikely that they would bust an FAR since they are issued a block of airspace to perform in that has pretty generous boundaries.

Ron - there is no requirement for the flight to be in radio communication or to do anything more coordinated than agree to fly in formation.  From ATC's perspective, a flight is a single aircraft.  #2 simply maintains position off lead at all times - that's really the only coordination required.  I'm also not talking about flying in waivered airspace (airshows), although the question would still apply (you can still bust an FAR flying in an airshow - i.e crossing the crowd line).

I recall seeing that somewhere that a formation flight is treated as one flight in the ATC system.  I don't know where I saw it, but I don't think that he's wrong about that.

In the eyes of the FAA, the wingmen are individually responsible if they violate an FAR, even if they are led into it by lead.
The controlling NTSB decision is:
3 N.T.S.B. 3302, NTSB ORDER NO. EA-1560, 1981 WL 40208
Administrator
v.
MERRELL R. GOSSMAN, EDWARD J. MODES, AND HOWARD MORGAN, JR., RESPONDENTS
Docket No. SE-4591, SE-4592, SE-4593
Adopted February 13, 1981

As the law judge stressed, each pilot-in-command of an aircraft “is
  directly responsible for, and is the final authority as to, the
  operation of that aircraft” and each pilot has the affirmative duty
  to comply with the minimum altitudes prescribed by section 91.79,
  which contains no exception for aircraft in formation following a
  leader.


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Is there a minimum separation between a landing aircraft and another crossing its runway?
I have just seen this video of what has been called a runway incursion at LEBL (my hometown airport). A russian jet initiates a go-around after seeing an argentinian plane crossing runway 02:
https://www.youtube.com/watch?v=1N5THRSp4hM
It's not clear (as of 2014-07-07 1400L) whether ATC gave clearance to cross the runway. Anyway, my understanding is that even with ATC clearance you are required to check for incoming traffic and hold short of the runway if such traffic exists.
Seems like the taxiing crew either didn't look for incoming aircraft or they estimated they had enough separation to cross the runway.
So, is there any regulated separation distance (time/space) that can be used to tell who was responsible for this conflict? It's solely based on pilots' criteria?

I think it's just no-one on the runway (past hold markers) from giving clearance to land to the landing aircraft leaving the runway. Existing traffic is allowed at time of issue as long a the pilot is advised and it will clear before arrival.

According to this article, "The airport's administrators say that the two airplanes were exactly where they were supposed to be, claiming there was enough distance between them".

According to avherald, it was an operational error, both a landing clearance and a crossing clearance were issued. They also further report there was a mixup in the operations, where the ground controller thought runway 2 was no longer in use issuing a crossing clearance without coordinating with the local controller.

Just to note that in the USA (unlike in Barcelona, apparently?) a crossing is allowed even if an aircraft has been cleared to land. The crossing must be completed, which means the aircraft is across the runway edge and nothing is restricting its movement beyond the opposite hold-short line, before the landing aircraft reaches the landing threshold.

When an aircraft has been given a clearance to land on a runway, that runway is exclusively reserved for the landing aircraft. (Except for LAHSO and "land after" operations, where only part of the runway is reserved for the landing aircraft).
That means that no other aircraft or vehicle should be on that runway. In this case, clearly something went unplanned. Either the crossing aircraft was not given permission to cross, the landing aircraft no clearance to land, or ATC mistakenly cleared both the landing aircraft and the crossing aircraft to access the runway.
Pilots should always check if the runway they are accessing is safe, and in this case the crew of the landing aircraft did apparently observe the incursion and aborted their landing. The crew of the crossing aircraft noticed the landing aircraft a bit late, but you hear their engines spool up as well as they cross. The sound of the go-around thrust arrives second later due to the difference in distance.
The crossing aircraft seems to be taxiing toward the rising sun so they may have been blinded and missed the fact that they were crossing a runway.

Good point about the rising sun!

In the US, with the right equipment, controllers can clear an aircraft to land while another is still holding for departure. Additionally, depending on aircraft weight class, they can issue a clearance that puts the arriving aircraft over the threshold while the previous arrival is still on the runway and as few as 3000 feet from the threshold. FAA JO 7110.65, section 3.10: http://www.faa.gov/air_traffic/publications/atpubs/ATC/atc0310.html

The U.S. uses "anticipated separation" whereas the rest of the world uses actual separation. In terms of runway separation, this means that in the U.S., a controller may clear two aircraft to land before either is anywhere near the runway. If you listen in on ATC at a class D airport with lots of flight training, it'll not be all too uncommon to clear two aircraft on downwind to land (the second has to have the first in sight, and is given the extra "number two" condition to the clearance). I don't think any other country in the world does this, but I might be mistaken.

A few months ago there were lots of planes in the pattern and the controller was clearing us to follow the plane in front of us and we were #n to land. There were so many of us that he lost track of which number the last one he cleared was. I don’t remember his exact words, but it was something like "Cessna XXX follow the Cherokee passing the numbers, you’re number five...no six... or whatever. "

I would think that for safety, if a LASHO clearance is given, any departing aircraft should need to acknowledge awareness of the incoming aircraft before being given clearance, and the departing aircraft pilot should be required to watch the incoming aircraft and be prepared for anything that it might plausibly need to do. Essentially, a LAHSO would give the incoming plane exclusive use of the entire runway, but ask that the pilot demonstrate as quickly as possible that it will definitely not be needed.  Is that how things are done, or are things more "optimistic"?

@supercat that would be a good separate question, but the quick answer is that things are more "optimistic"—a LAHSO clearance restricts the landing aircraft so that the runway available to them is much shorter. It is the pilot's responsibility to determine if they can accept landing on such a shortened runway, and if they feel they cannot, they should not accept the LAHSO clearance.

@randomhead: The amount of runway an arriving aircraft is going to need is ultimately going to be determined by Sir Isaac Newton, possibly in cooperation with Murphy, and not by anything ATC or pilots may do or say.  Until a plane's wheels hit the runway, a pilot will have no way of knowing whether brakes or thrust reversers will actually do anything.  If a pilot is asked to hold short of a crossing runway if possible, and a plane takes off across that path as soon as the incoming plane has stopped, that would allow the latter plane to take off faster than if the incoming plane...

...would come to a stop nearer or past the intersection.

@supercat that may be so, but from a rules-and-procedures standpoint (at least in the USA) if a pilot accepts a LAHSO clearance ATC treats it as given that they will stop before the crossing runway, and will therefore use the crossing runway however they like. (ATC is supposed to exchange traffic so the pilots know what's going on.) Is it possible that a pilot could violate a LAHSO clearance? Sure. But they shouldn't, because they have performance data and weather information to inform their decision to accept it in the first place.

@randomhead: Is there any means by which pilots can reliably predict when thrust reversers or brakes will fail?

@supercat let's move to chat.


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Does autopilot disconnect when a danger alarm like GPWS triggers?
I was wondering if any of the (E)GPWS callouts would make the autopilot disconnect?
If the Alpha Protection is active (like in Bilbao, 2014) would it disconnect? That would give PF full control of the aircraft and could help to recover from the upset, correct?

Comments are not supposed to be 'thank you' or the equivalent... but ... thank you for not joining the masses and mass media by condemning the pilot. It seems everyone 'knows' his mental state is involved, even before the FDR is (if ever) recovered.

I heavily reworded the question to remove non necessary reference that would invite speculations (that would be off-topic) and I aimed in keeping the original underlying question untouched. If you feel that this has been excessive, you can revert my edit.

It should be noted, that the Bilbao incident was caused by flight envelope protection, which is different system from autopilot and never disconnects unless the air data units indicated fault or are switched off manually. The EGPWS alert procedure from the answer below even relies on it by saying "Pull up to full stick and maintain", which would cause a stall without flight envelope protection.

This is the Quick Reference Handbook procedure from an old A320 training manual.

(The EGPWS procedure is a memory item, pilot's are not expected to look this page up when they encounter a EGPWS warning)
The first two sub items answer your questions. The autopilot needs to be switched off manually and the instruction is to pull up to full back stick and maintain. The Alpha protection will prevent the aircraft from stalling, that is why the stick can be maintained at full back deflection.
Airbus' safety magazine FAST #23(PDF) giving guidance on flying protected aircraft, specifically advices pilots to apply full backward stick deflection in GPWS situations since the alpha protection will prevent the aircraft from stalling and the resulting flight path is the most effective way away from danger.
To illustrate a possible the effects of Alpha protection in an (E)GPWS situations, let's go to Bilbao again, but now in March 2001(PDF). An A320 on final approach encountered a wind shear causing the aircraft to descent fast. This caused the GPWS to trigger a warning. The pilot applied TOGA power and back stick deflection, but the Alpha protection predicted the aircraft to stall and prevented a higher nose attitude. As a result the aircraft didn't stall but crash landed on runway threshold. This accident demonstrates that the GPWS does not affect the flight envelope protection system.

No, the EGPWS is a warning system, and does not typically interface with the autopilot. The first step in reacting to EGPWS (or most TCAS) warnings is to disconnect the autopilot & autothrottles and fly manually, but this isn't accomplished by the EGPWS itself.


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Is it a mistake or standard procedure to lit the landing lights only on very short final?
Yesterday I was spotting at Barcelona International (LEBL). I noticed that at least two airliners were approaching with their landing lights OFF, just to light them on very short final (about 0.4NM from runway threshold).
I thought landing lights were required to be ON at all times below 10000 feet. Am I wrong? Is there any situation when landing lights are not required below 10000 feet?
Visibility was excellent, I'm going to see if I can find the actual METARs but I would say CAVOK conditions. see the METARs:

LEBL 161630Z 17007KT 140V210 CAVOK 19/11 Q1019 NOSIG
LEBL 161700Z 20007KT 150V230 CAVOK 19/11 Q1019 NOSIG
LEBL 161730Z 22007KT 170V240 CAVOK 19/12 Q1019 NOSIG
LEBL 161800Z 21007KT CAVOK 18/12 Q1019 NOSIG
LEBL 161830Z 20005KT 170V230 CAVOK 18/12 Q1020 NOSIG
LEBL 161900Z 21005KT CAVOK 17/12 Q1020 NOSIG

They probably were on, you just couldn't see them being on from your angle. I've never heard of there being a requirement to have landing lights on below a certain altitude anyway.

@GdD I was few meters off the extended runway centerline (On top of the hill here: https://goo.gl/maps/hxeXU7pZUts). One of these airliners got LED-like lights and suddenly they were lit.

As I said, maybe it was your angle. If the airplane was crabbing away from you would not necessarily see the light

FWIW, standard practice at the two 747 carriers I worked for in the 1990s was to turn the landing lights on descending through 10,000 feet on the arrival, turn them off climbing past 10,000 on departure. However, to the best of my knowledge, at least back then, there was no regulation stating that this was required. It was just a standard operating procedure and was thus in our check lists.

In the US, having landings lights on below 10,000 is "encouraged" by the FAA and I've often heard it's standard practice for airlines as part of their OpSpec (as Terry mentioned). But there's no specific regulation that requires it. I have no idea what the situation is under EASA regulations.

What was the weather like?  Visibility and ceiling?

@wbeard52 see updated question :)

It is not an ICAO requirement to operate landing lights whenever you are below 10,000 FT. The mandatory aircraft lights you will see in regulations is strobe lights, nav lights and anti collision beacon lights.
It is standard operating procedure at several airlines to only turn on the landing lights when a landing clearance is received by air traffic control. This is most likely what you have observed. The landing clearance is usually given at very short final, and so crews will turn on the landing lights on very short final (unless you are in FAA territory, where multiple aircraft can be cleared to land on the same runway at the same time ...)

I can't speak for Spanish or other international operations, but in the United States, landing lights are only required for use at night when carrying passengers for hire.  It is, however, a common courtesy to use landing lights in or around congested airspace at or below 10,000 feet, day or night, to make it easier for other aircrews to see your aircraft.
This also depends on the configuration of the aircraft.  Some aircraft only have landing lights on the retractable landing gear, and, unless the gear is extended, they cannot be used.


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What does the ATC instruction "Make left traffic, runway 19L" mean?
I'm playing Prepar3D and when coming in for a landing I'm usually told something like Make left traffic, runway 19L. I'm not sure how to interpret this because I'm not a pilot.
Should I go to the left of 19L for my downwind leg so the runway is to my right, or should I go to the right, with the runway on my left?
Also with parallel runways should I go to the left of 19L exactly or is it the left of 1R? I'm very confused!

'Left' or 'right' traffic means that when you are flying the traffic pattern, all turns are to that direction.
The wikipedia article on traffic patterns isn't bad, and has some decent graphics, including this one from the FAA's Handbook of Aeronautical Knowledge:

The top pattern is left traffic, while the bottom pattern is right traffic.

Note that being on a left parallel runway (like 19L) does not mean you're always going to get a left pattern. I have on a few occasions been told to make left traffic from a right runway because of nearby traffic. This is why it's important to a) listen carefully to tower, b) read back all instructions, and c) check the other runway for traffic. Never had instructions corrected (I've had them repeated back to me to confirm after I read them back) and never had to stop for someone else, but it feels weird to do it, and I was never quite happy until I was either back on the ground or flying out.


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What appears on EGT Gauge if the mixture is rich or lean?
I have some questions on interpreting Exhaust Gas Temperature (EGT) readings.  Can you give me some input on:

What appears on EGT Gauge if the mixture is lean or rich?
what is the normal range, high range, and low range for EGT?
What is the relationship between the EGT and rich or lean
mixture?

The range for EGT will depend on the engine/aircraft.

Since your profile photo has you standing next to a piston aircraft I'm going to assume you're talking about piston engines :)

The exact number on an EGT gauge is usually meaningless: The Alcor EGT gauge you'll find on many aircraft has no temperature markings on it - just 25-degree divisions, and a yellow "reference pointer" which the pilot sets to the maximum observed EGT:

The notable exception to this is turbocharged engines which have a Turbine Inlet Temperature (TIT) limit to protect the turbocharger. For engines with exhaust gas / turbine inlet temperature limits these limits will be specified in the aircraft's Pilot Operating Handbook, and usually marked with green/yellow/red arcs on the relevant gauges.

Exhaust Gas Temperature (EGT) provides pilots a way of monitoring the fuel/air mixture in the engine. It uses the stoichiometric mixture (where Fuel and Air are perfectly balanced so that there is no unburned fuel and no unburned oxygen at the end of the combustion event) as a reference: At this mixture the EGT is at its hottest ("Peak EGT"). Making the mixture richer or leaner will reduce the EGT, and all other mixture settings are described in terms of "Degrees Rich of Peak" or "Degrees Lean of Peak".
Refer to the handy chart from Lycoming below for the remainder of this discussion:

EGT and Mixture
When we talk about mixture in piston aircraft engines we're generally interested in one of two things: Best Economy - getting the most power from the engine for the least amount of fuel, or Best Power - Getting the most power from the engine regardless of fuel burn.  We're also interested in something called Detonation Margin, which in simple terms means "how likely is this mixture to explode rather than burn nicely?"
As you can see on the Lycoming chart above the EGT provides us a way of finding those mixtures.
Best Economy Mixture
The "Best Economy" range begins at peak EGT, and continues on the lean side until the engine won't run smoothly anymore (usually the limit is about 100-150 degrees Lean of Peak).
Operating the engine at Best Economy mixture provides the most power for the least amount of fuel, and thus the longest endurance. It comes at the cost of a reduced detonation margin on the fuel/air mixture - operating at high power settings with a best economy mixture increases the chance of detonation.

Most aircraft/engine manufacturers recommend Best Economy mixture for power settings below 75%, in part to reduce the risk of detonation.

The Red Box - Where you don't want to run your engine.
The area of the chart from peak EGT to about 100 degrees Rich of Peak is often referred to as "The Red Box" -- in this range the fuel/air mixture has a low detonation margin, and the combustion event is producing the most internal stress on the engine components (cylinders, pistons).
As you can see from the Lycoming chart the Cylinder Head Temperature (CHT) peaks in this range, and there is a risk of exceeding the CHT limits and seriously damaging your engine by operating in this range for extended periods of time, particularly at high power settings.
Best Power Mixture
From approximately 100 degrees Rich of Peak to 200 degrees Rich of Peak is the "best power" range - in this mixture range you can safely run the engine at high power settings (from 75% of rated power to full rated power) with limited risk of detonation. The engine is producing the most power it can in this range, which is useful if you need to climb over an obstacle in your flight path.
For simple aircraft with fixed-pitch propellers the "Best Power" mixture can also be found by adjusting the mixture to obtain maximum RPM for a given throttle setting.

Operating in the "Best Power" range is not without risks - in particular, detonation is still possible at high power settings. The same Lycoming manual that I pulled the chart above from advises monitoring CHTs when using Best Power mixture settings.

Less Interesting Mixtures
There are two ranges on the chart I did not discuss above - they are what I call the "Less Interesting Mixures"
Leaner than Best Economy
As you continue to lean the engine past the "Best Economy" range you will notice a sharp drop-off in power. This drop is so precipitous that you will no longer be saving fuel as you leave the Best Economy range: You will be burning more fuel per unit of horsepower produced than you were in the economy range.
Eventually the engine will run rough as the mixture becomes too lean to burn, and at the very extreme end the engine will quit, starved of fuel.
Richer than Best Power
Mixtures richer than Best Power don't produce the same precipitous drop in horsepower, but they consume substantially more fuel per unit of horsepower produced. They also have other negative side effects, like producing black sooty exhaust that will get all over the belly of the aircraft.
As the mixture gets richer it will eventually become too rich to burn, and the engine will begin to run rough as it did being leaned. At the far extreme the engine will become flooded, and cease to run.

Recommended Reading / Viewing

Your engine manufacturer's operating instructions
Mixture Magic (John Deakin)
EGT, CHT, and Leaning (Mike Busch)
Leaning Basics (EAA/Mike Busch) (video)
Leaning: The Advanced Class (EAA/Mike Busch) (video)

what does each pointer on EGT gauge indicate? and what does it mean by 25 degrees division? Thank you

@WilliamHan I assume you're referring to the Alcor gauge photo above: This is a "single-probe" gauge, so it shows you the EGT of whatever cylinder it's attached to. The white pointer indicates the temperature, and the yellow one is a reference mark the pilot positions using the knob at the bottom of the gauge (it's used to mark peak EGT when you observe it). Each tick mark on the scale is 25 degrees Fahrenheit (25°F/DIV), and the long ticks are 100 degrees. That allows you to determine how many degrees lean or rich of peak EGT you are.

Which Lycoming manual is that chart from?

Figure 3-1. Representative Effect of Fuel/Air Ratio on Cylinder Head
Temperature, Power and Specific Fuel Consumption at Constant RPM and
Manifold Pressure in Cruise Range Operation, from Operator’s Manual
Lycoming O-360, HO-360, IO-360, AIO-360, HIO-360 & TIO-360 Series, 8th Edition, Part No. 60297-12, dated October 2005. Page 3-7.


text:
If you replaced jetfuel with hydrogen could the aircraft engine work on hydrogen?
I know that hydrogen has a reaction with oxygen like with jet fuel, but could the engine run on hydrogen.

While it's certainly possible to do so (jet engines will run on almost anything that burns - see the answer on the duplicate) hydrogen has a few disadvantages which make it less than attractive as an aviation fuel.

Also, aside from its tendency to combust at inopportune times, hydrogen is a pain to store. It either has to be compressed to very high pressures or take up a lot of space. Or both.

@voretaq7 If this is a duplicate, the other question should be edited to be more generic.

@digitgopher A question need not be an exact duplicate to be closed as such. See http://aviation.stackexchange.com/help/duplicates for more information.

Your fuel tank will get MUCH bigger and heavier. Hydrogen has great energy density by mass (eg kWh/kg)...until you contain it. To store H2 at STP takes a LOT of volume. Liquid H2 (cryo storage) isn't practical for general use, and even as a liquid H2 has far worse volumetric energy density than petrofuels. High pressure gas storage means massy containers with thick walls and the volumetric density is far worse than for liquid H2. See http://www.tinaja.com/glib/energfun.pdf - table on p.2. Funnily enough, a liter of petrofuel has more H2 in it than a liter of liquid H2.


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Why can't horizontal stabilizers be longer than they are today?
I've wondered this question because if the horizontal stabilizer is longer than that means more lift. My guess to this question would be the result of wing tip vortex strength on a longer wing

What's the question?

Its why the back wings or horizontal stabilizers aren't any longer than they are today.

Do you know that they provide negative lift? They provide stability at the cost of drag. The shape is optimised to provide low drag whist providing enough longitudinal stability

Is the drag caused by wing tip vortex

@Ethan: No, drag is caused by generating lift. By any means. The wing tip vortex is also caused by generating lift, though if it is by other means than wing, it is not a wing-tip vortex, but something else-vortex.

Actually there is drag caused by lift and its called wing tip vortex, which forms by the high pressure area of the wing coming up on the low pressure area causing a rotation which is called wing tip vortex so I am wondering if wing tip vortex forms with a horizontal stabilizer same as the main wing.

@Ethan, yes a horizontal stabilizer can cause a tip vortex as well. See this video. Not all drag causes a vortex. Profile drag is caused by friction of the airflow over the skin of the surface and does not result in a vortex.

What DeltaLima said. The 'lift' generated by the horizontal stabilizers is a downward force for stability, not an upward one. Increasing that force make the plane less efficient, not more (and this would still be the case even if it generated no drag at all in the process of generating that downward force... the downward force itself is inefficient.)

@DeltaLima, Ethan, the primary source of drag on a lift-generating surface is always going to be induced drag, not profile drag or a wingtip vortex.

@egid the wingtip vortex is the result of the induced drag. See the article you linked to :-)

Yeah, but my point is that the vortex is a byproduct of drag, not the sole cause, as OP seems to imply.

Something similar I have wondered about is why the HT does not have a higher aspect ratio. With the same area (read lift) but higher aspect ration, it will produce less induced drag. My first thought is that the tail structure becomes to heavy. Perhaps it is something we will start to see with the advent of new advanced materials?

Why are you assuming they can't be longer?

The stab in that picture is very foreshortened.

The horizontal stabilizers can be longer, they just don't need to be any longer than they are.
Each additional square inch will add induced drag and parasitic (form / profile) drag which costs fuel so they're not made any bigger than necessary to provide adequate control of the plane.

On most aircraft, the horizontal surfaces in the rear are horizontal stabilizers. These surfaces actually provide negative lift, which balances the center of gravity being forward of the center of the lift force. This balance of forces provides natural stability in a simple way, which is why is is the standard design for both large and small aircraft. Of course this negative lift is working against the main wing, which increases the drag, so this surface is kept as small as possible to provide sufficient stability with as little drag as possible.
There is an aircraft layout called tandem wing, where there are two wings in a tandem configuration that both provide upwards lift.

Ehh, no. These surfaces 'can' provide negative lift which can be desirable when you want to push the tail down (to pull the nose up.) but equally they can generate positive lift to pull the tail up (and the nose down). They are usually designed to be lift neutral is most circumstances to reduce drag and fuel consumption.

@PaulSmith: No, to make the rear wing lift-neutral would be inefficient and produce too much stability. Normally, lift on the rear wing is less per unit of area than on the forward wing, but still positive, even at high speed. Just look at the position of the wings - the cg is between both, so both need to create lift.

Also, canards.

Paul and Peter are talking about two different things - Paul's referring to horizontal stabilizers on conventional-layout aircraft (as discussed in the first part of fooot's answer) while Peter is talking about the rear wing of a tandem-wing aircraft.

The tail surfaces of an aircraft are also called the "empennage", a term originating from the French word for the fletching of an arrow. The term thus indicates the purpose. The horizontal and vertical stabilizers are exactly that, stabilizers. Their purpose is to keep the plane's fuselage in line with the relative wind caused by the aircraft moving through the air. Without them, the plane could easily enter a sideslip or a tumble. They also provide pitch and yaw control by redirecting the relative wind upward or downward, having the opposite effect on the airframe (Newton's third law).
They are not intended to generate lift to counter gravity, and in many cases the horizontal stabilizer does just the opposite, providing a downward force on the back of the aircraft through a combination of negative pitch and "downwash" of air from the wings. This keeps the nose up during forward flight, compensating for a slightly nose-heavy weight distribution which in turn provides desirable flight characteristics such as the tendency to nose-down in a stall (if you're going to fall out of the sky, you might as well fall in an attitude that restores a low angle of attack and thus has the potential for you to recover).
Therefore, in a traditional configuration, they aren't any bigger than they are because they don't have to be. A larger horizontal stabilizer will increase drag due to the greater surface area and volume of displaced air, for no real gain. Potentially the control surface area could be increased, but there is a limit to how big they can be before the forces acting on the control surface in a deflected position exceed the materials strength of the control surface or the airframe. Even before that, larger control surfaces make the plane more sensitive to stick/yoke input, which is useful for a fighter or aerobatic airplane, but potentially deadly for a plane designed for use by the "everyman" pilot.

As already noted, they  can be, but are not, in order to reduce drag.
In general, the horizontal stabilizers in present generation of aircrafts are smaller than their predecessors. This is a result of the advances in design the aircraft with the introduction of fly-by-wire systems.
The horizontal stabilizers are designed to give stability to the aircraft by giving a negative pitching moment. The aircraft wing, in itself is unstable. As lift is generated, the wing pitches up, which increases the angle of attack, increasing lift. This process goes on till the wing stalls. The horizontal stabilizer is effectively a smaller wing located at the other side of the center of gravity at a longer distance, negating this pitch up moment of the main wing.
So, basically the horizontal stabilizer produces a positive lift, but a negative pitching moment. The bigger the horizontal stabilizer is, more the lift and stability, but also the drag.
One way to reduce the drag is to have a smaller horizontal stabilizer, but this reduces stability, requiring the pilot to continuously adjust the controls to fly the aircraft. However, the introduction of computer controlled controls (fly-by-wire systems) meant that the aircraft could be unstable, with the computer adjusting the controls continuously to achieve stable flight.
As a result, the aircraft designed after 1990's mostly have fly-by-wire control systems with smaller horizontal stabilizers, resulting in less drag and decreased fuel consumption.
As an example, compare the horizontal stabilizers of DC10 and MD11.
Source: Boeing 757 Maya
The MD11 was based on DC10, with stretched fuselage and increased wingspan, however with a smaller tailplane. This was achieved using a (partially) computer controlled horizontal stabilizer. As can be seen from the image, the horizontal stabilizer in the MD11 was smaller than the DC10, though the aircraft was larger.
So, the reason for smaller horizontal stabilizers is to reduce weight and drag and this is achieved mainly through the use of computer controlled control surfaces. Because the smaller stabilizer relaxes the stability, even though it might have enough control due to the longer moment arm:

Relaxed stability designs are not limited to military jets. The McDonnell Douglas MD-11 has a relaxed stability design which was implemented to save fuel. To ensure stability for safe flight, an LSAS (Longitudinal Stability Augmentation System) was introduced to compensate for the MD-11's rather short horizontal stabilizer and ensure that the aircraft would remain stable. However, there have been incidents in which the MD-11's relaxed stability caused an "inflight upset."

Ist't the tail of the MD-11 smaller because it has a longer lever arm? The tail volume of both aircraft should be quite the same. Also, any FCS cannot help to trim the aircraft over a wide range of cg positions, and it is this trim range which drives tail surface volume.

Concorde designers took a different approach: they removed the horizontal tail planes to decrease drag as much as possible.
Every unnecessary thing (pod/pylon/etc.) on the outside of the fuselage or under the wings add drag, even without generating lift.
Another historical example is the MD-11, evolution of the DC-10. If you notice, the MD-11, even if longer and heavier, has smaller tail planes for better cruise performance.

I notice a slight bulge in the tail of the Concorde, about where the rear horizontal stabilizers would be. I would have guessed that it is there for a similar reason, albeit quite small.

@KRyan what bulge? If you're referring to the two "bulges" on the vertical stabilizer, they're just the fairings for the rudder actuators. If you look at both sides, you'll notice they're not symmetrical: the left one moved the lower part of the rudder, while the right one moved the upper part.

ah, right you are.

The horizontal tailplane can be longer, in order to keep the tail area constant, the chord would be reduced accordingly. The higher tail aspect ratio would result in a higher root bending moment, therefore a heavier construction.
A higher aspect ratio reduces induced drag, very desirable in the main wing but of secondary importance in the tailplane. Induced drag is proportional to lift, and lift generation of the tailplane is minimised anyway, for minimum trim drag.